The present invention relates to a protecting device for a fail-safe operation in the case of a failure, an accident, etc. in an electromobile incorporating a synchronous motor therein as a power source.
The development of electromobiles has rapidly progressed as a countermeasure against environmental problems, and the direct current motor power source of an increased number of the newer electromobiles has been replaced with an alternating current motor due to its inherent advantages such as ease of maintenance and the like. Particularly, a synchronous motor using a magnet as a rotor is highly efficient, and is therefore especially suited for use in electromobiles. The synchronous motor of this kind has conventionally been widely used in factory automation or industrial fields, and the basic controlling system of the synchronous motor used in electromobiles is almost the same as that used in factory automation or industrial fields.
However, because of the undeniable fact that human lives are exposed to a high risk in vehicles, it is necessary to take all possible fail-safe measures.
FIG. 4 is a circuit diagram of an electromobile in one proposed example, in which reference numerals represent respectively: 1 a control device; 2 a PWM (pulse width modulation) inverter; 3 a motor such as a synchronous motor or the like; 4 an encoder coupled to a rotary shaft of the motor 3; 5, 6 current detectors for detecting a phase current of the motor 3; 7 a primary battery for supplying electricity to the motor 3 via the PWM inverter 2; and 8 a control battery for supplying a control current to the control device 1 via a key switch 9.
When a driver turns on the key switch 9 of the electromobile, the control device 1 is connected to the motor 3 via the PWM inverter 2, so that a current to the motor 3 is commutated at a suitable timing. In this case, the control device 1 controls the PWM inverter 2 so as to a supply a torque current to the motor 3. The motor 3 rotates when it receives electricity from the primary battery 7 of V.sub.Batt voltage via the PWM inverter 2. The positional data of a rotor of the motor 3 and the speed of the motor 3 are sent back to the control device 1 from the encoder 4 coupled to the rotary shaft of the motor 3. At the same time, the phase current of the motor 3 is detected with the use of the current detectors 5, 6 or the like and fed back to the control device 1. The control device 1 properly controls the rotation of the motor 3 based on the above fed-back signals and signals from an accelerator sensor, etc.
In the electromobile, outputs of the accelerator sensor interlocking with an accelerator pedal, namely, accelerator sensor signals which rise, for example, linearly in proportion to the opening degree of the accelerator and, output signals of the encoder which indicate the present rotating speed of the motor are inputted to the control device 1. The control device 1 in turn detects the difference between the accelerator sensor signal instructing the required rotating speed of the motor 3 and the output signal from the encoder 4 indicating the present rotating speed of the motor 3, to thereby, effect control by supplying a torque current to the motor 3, corresponding to the detected difference. The accelerator sensor signal and the torque current obtained by calculations as above are monitored for a fail-safe operation. The torque current I.sub.q to be outputted when the accelerator sensor signal is zero cannot hold I.sub.q &gt;0. Therefore if the condition satisfying I.sub.q &gt;0 arises it is considered abnormal, necessitating a safety control. To secure safety, it is desirable to stop the control of the motor 3.